Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Non-volatile memory is memory that can retain its stored data for some extended period without the application of power. Common uses for flash memory and other non-volatile memory include personal computers, personal digital assistants (PDAs), digital cameras, digital media players, digital recorders, games, appliances, vehicles, wireless devices, mobile telephones and removable memory modules, and the uses for non-volatile memory continue to expand.
Flash memory typically utilizes one of two basic architectures known as NOR Flash and NAND Flash. For example, a NAND flash memory device is a common type of flash memory device, so called for the logical form in which the basic memory cell configuration is arranged and accessed. Typically, the array of memory cells for NAND flash memory devices is arranged such that memory cells are coupled together in series (e.g., coupled source to drain) to form strings of memory cells. Changes in threshold voltage of the memory cells, through programming (which is sometimes referred to as writing) of charge storage structures (e.g., floating gates or charge traps) or other physical phenomena (e.g., phase change or polarization), determine the data value of each cell.
To meet the demand for higher capacity memories, designers continue to strive for increasing memory density, i.e., the number of memory cells for a given area of an integrated circuit die. One way to increase memory density is to reduce the feature size of individual memory cells. Another method has been used to form NAND strings vertically along semiconductor pillars, which act as channel regions of the NAND strings. A number of undesirable effects can occur however when operating memory devices comprising these vertical structures, such as charge leakage and other phenomena which can introduce uncertainty and reduce reliability during various memory device operations, such as programming and/or sensing operations, for example.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative methods of operating various memory device architectures.